Kerry D. Wong wrote an article on how to modify a CP2102 module as an Arduino programmer:
To make it work with the Arduino bootloader, one easy approach is to disconnect the RST header pin from CP2102 pin 9 and connect it to the DTR pin (pin 28) instead. While in the Arduino schematics, the reset pin is connected to the ATmega328P pin 1 (RST) via a 100 ohm resistor, this connection is not strictly needed as pulses from the DTR pin (connected to ATmega328P pin 1 via a 100nF capacitor) will reset the MCU properly during programming. The two pictures below illustrate the connection between the module RST header and the RST pin of CP2102.
Yup, had/have the same problem. Unfortunately, a rather strong distaste for that sort of bodging prevents me from doing the same (the pin is not accessible as a PCB trace sadly). But for anyone who wants to go for it – more power to you… :)
I also wrote something about the modification of a cheap FTDI adapter. Basic exact the same thing as Kerry.
see it on: http://www.bluemotica.nl/index.php/en/arduino/arduino-faulty-ftdi-adapter
Instead of modifying the USB-TTL adapters, I modified the AVR board and the avrdude software to reset the AVR with a break signal. This way just Rx, Tx, Gnd and Vcc are needed.
http://nerdralph.blogspot.ca/2014/02/zero-wire-serial-auto-reset-for-arduino.html
Instead of modifying the USB-TTL adapter I modified the AVR board to reset with a serial break signal.
http://nerdralph.blogspot.ca/2014/02/zero-wire-serial-auto-reset-for-arduino.html
@Ralph: Thanks for the idea, although to be fair I think I’d rather implement it as a tiny ‘M-F pin strip adapter’ between the CP2102 and any Arduino. It would be indeed exceedingly useful to have official support for this – too bad the Avrdude guy is being unreasonable (it’s really not like half the internet using cheap DTR-less dongles would profit or something, right…).
@Max: your point about modifying just the dongle is a valid one. So what I’ll do is a version with the circuit on the USB-TTL adapter, with a breakout for the RST connection.
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